Carl Ludwig: the man, his time, his influence.

Carl Ludwig (1816-1895) was the driving force in the foundation and development of scientifically based and experimentally oriented physiology against natural philosophy and vitalism that prevailed during the first quarter of the 19th century in Germany. He was the representative of a small group of young, highly talented and dynamic physiologists aiming at implementing the laws of physics and chemistry as the only active forces in physiologic processes. These "organic physicists" included Emil du Bois-Reymond (1818-1896), Ernst Brücke (1819-1892), and Hermann Helmholz (1821-1894). Carl Ludwig wrote the program of this group in the form of a textbook of physiology that was considered revolutionary, provocative and premature. His academic life, his inventions and discoveries, his scientific achievements, his influence and his personality are reviewed. Since every person can be viewed only in the context of his time, the political background, the economic and social situation, the conditions for science and research as well as the cultural climate that were characteristic for the decisive years of Carl Ludwig are described to some extent. It is shown that Carl Ludwig and his contemporary organic physicists lived and grew into a science- and research-oriented period which had been prepared and paved by men like Johannes Evangelista Purkinje (1787-1869), Ernst Heinrich Weber (1795-1878), Alfred Wilhelm Volkmann (1800-1877), Johannes Müller (1801-1858) and Gustav Theodor Fechner (1801-1887). They benefited from this enormous scientific development and contributed to it to a large and significant extent so that it ultimately turned out to be the most productive and influential period in the history of German physiology. Some of the numerous scholars who had studied with Carl Ludwig carried his approach to physiology into the 20th century: Adolf Fick (1829-1901), Otto Frank (1865-1944), Iwan Petrowitsch Pawlow (1849-1936) and Henry Pickering Browditch (1840-1911).